1. Field of the Invention
The present invention relates to a surface shape measurement apparatus and an exposure apparatus.
2. Description of the Related Art
There is conventionally known a scanning exposure apparatus configured to expose an original's pattern onto a substrate via a projection optical system using a step-and-scan manner that synchronously scans the original and the substrate. See, for example, U.S. Pat. No. 4,861,162. Since it is necessary for the scanning exposure apparatus to focus the substrate surface onto an image surface position of the projection optical system on a real time basis during the exposure, a surface position (height) and tilt of the substrate are measured by using obliquely incident light before a position to be exposed reaches an exposure slit as a scan area. See, for example, Japanese Patent Laid-Open No. 06-260391.
A method for separates white interference light that contains information of the substrate's surface shape into a plurality of interference light beams each having a single wavelength, for photoelectrically converting the interference light beams, for performing a fast Fourier transformation (“FFT”) for the obtained plurality of interference signals, and for obtaining the substrate's surface shape is applicable to the measurement of the surface shape of the substrate. The measurement principle is disclosed in Chih-Che KUO, et al., “Signal Processing for Wavelength Scanning Interferometer,” Journal of the Japan Society for Precision Engineering, Vol. 69, No. 6, 2003, p. 831. As a method for separating the white interference light into a plurality of interference light beams each having a single wavelength, there are known a method for preparing a plurality of glass filters having different wavelength transmission characteristics and for changing the combination, and a method for making variable a wavelength of a laser as a light source.
Due to the recent demand for a high resolution, focus and tilt measurements require a high precision, and the conventional measurement method that utilizes the obliquely incident light cannot obtain the given measurement precision due to the influence of a peripheral pattern on the substrate and uneven thickness of the resist. A problem caused by a longitudinal structure of the substrate can be solved by setting an incident angle upon the substrate to 80° or larger, but the optical system become complex, large, and vulnerable to the disturbance because the optical path length increases.
On the other hand, the surface shape measurement apparatus that utilizes the white interface light and uses a glass filter for light splitting requires a movable part in a part of the optical system and thus becomes complex. In addition, a method for making variable an oscillation wavelength of the laser also makes complex the surface shape measurement apparatus.